1. Field of the Invention
This invention relates in general to air bearing sliders for use with recording media and more particularly, to a method and apparatus for improving file capacity using different flying height profiles.
2. Description of Related Art
Conventional magnetic disk drives are information storage devices which utilize at least one rotatable magnetic media disk with concentric data tracks, a read/write transducer for reading and writing data on the various tracks, an air bearing slider for holding the transducer adjacent to the track generally in a flying mode above the media, a suspension for resiliently holding the air bearing slider and the transducer over the data tracks, and a positioning actuator connected to the suspension for moving the transducer across the media to the desired data track and maintaining the transducer over the data track during a read or a write operation.
In magnetic recording technology, it is continually desired to improve the areal density at which information can be recorded and reliably read. Because the recording density of a magnetic disk drive is limited by the distance between the transducer and the magnetic media, a goal of air bearing slider design is to "fly" the air bearing slider as closely as possible to a magnetic medium while avoiding physical impact with the medium. Smaller spacings, or "fly heights", are desired so that the transducer can distinguish between the magnetic fields emanating from closely spaced regions on the disk.
Zone bit recording can provide significant performance and capacity improvements in magnetic disk storage files. In order to facilitate this technology, it is desirable to maintain a constant spacing between the read/write head and the disk across all the zones, from the ID radius to the OD radius of the disk. It is also desirable to fly as low as possible across the data zones to increase amplitude and resolution and further increase areal density and file capacity. However, low fly height causes concerns over mechanical reliability in the file, for both start/stop life and long term flyability.
Constant flying heights across the data zones presents a substantial challenge to slider design because the air velocity created by the rotating disk varies in both magnitude and direction relative to the air bearing slider at all radii. This is further exacerbated in rotary actuator files, since the air bearing slider skew angle also varies across the data zone from ID to OD.
An air bearing slider also experiences fly height variations due to roll. For an air bearing slider with zero skew relative to disk rotation, roll is a measure of the angle formed between the surface of the disk and a plane holding the longitudinal and latitudinal axes of the air bearing slider. Variations in roll occur when a resiliently mounted slider experiences a skewed air flow or the actuator experiences head to disk contact. Insensitivity to roll variations is a crucial requirement of air bearing sliders.
Variations in the crown of an air bearing slider can also lead to variations in fly height. Crown is a measure of the concave or convex bending of the air bearing slider along its longitudinal axis. Crown develops in sliders because of surface stresses that arise during the fabrication and suspension bonding processes. These stresses are not well controlled and therefore lead to sliders with relatively large variations in crown. Also, an individual slider can experience variations in its crown due to temperature variations that occur during the normal operation of a recording disk drive. For these reasons, it is important that the flying height of an air bearing slider not vary substantially as a result of variations in crown. Furthermore, an air bearing slider with a non-zero crown is the equivalent of a flat slider flying over a disk having small amplitude, long wavelength undulations. Therefore, since all disks have some degrees of waviness, an air bearing slider that is less sensitive to variations in crown is also less sensitive to imperfections in the flatness of the recording disk it is flying over.
Finally, an air bearing slider experiences varying conditions during the high speed radial movement of the actuator as it accesses data on various portions of the disk. High speed movement across the disk can lead to large values of slider roll and skew and a resultant variation in fly height. This is yet another reason that an air bearing slider must be insensitive to changes in roll and skew.
Typical taper-flat type sliders cannot satisfy the constant spacing requirements for zone-bit recording. For most rotary actuator configurations, the taper-flat slider flying height increases rapidly as the head is moved out from the ID. As it approaches the middle of the data band, it reaches a maximum spacing, which may be up to twice as large as the initial ID flying height. From there, the clearance drops as the air bearing slider moves toward the rim of the disk.
When any of the above described variations in fly height occur, they may result in contact between the air bearing slider and the rapidly rotating recording medium. Any such contact leads to wear of the air bearing slider and the recording surface and is potentially catastrophic. Prior art slider designs have attempted to avoid this problem by addressing one or more of the above described sensitivities, so as to produce an air bearing slider with uniform flying height under the varying conditions that may be experienced by the air bearing slider.
One example of an air bearing slider which is designed to be insensitive to roll, crown, and skew is disclosed in U.S. Pat. No. 5,396,386, issued to Bolasna et al., entitled "ROLL INSENSITIVE AIR BEARING SLIDER", and is incorporated by reference herein. The air bearing slider described by Bolasna et al. includes a pair of substantially co-planner side rails. A recess section is open at both the leading and trailing ends of the air bearing slider while each side rail has a tapered section or etched depth at the leading edge of the air bearing slider. One rail carries the transducer and it extends from the entire length of the air bearing slider body. The rail without a transducer extends from the leading edge towards the trailing edge, but does not extend all the way to the trailing edge. Under some skew, accessing, and head to disk contact conditions, resulting slider roll causes the flying height of the inactive rail to drop. By proper selection of the length and width of the inactive rail, the roll is biased such that the fly height of the inactive rail remains higher than that of the active rail even under worst case conditions. Therefore, minimum slider to disk spacing is larger than it would be for an air bearing slider design in which all rails extend the entire length of the air bearing slider.
Greater data densities require lower and lower flying heights which in turn demand smoother and smoother disks. However, increased disk smoothness results in increased head-disk stiction which can result in increasing the torque required to start the disk drive. In some disk drives, this problem is partially solved by texturing portions of the disk, for example the start-stop zone. The fly height of the magnetic head element is maintained fairly constant over the entire disk to maximize the storage capacity of the disk drive. With a flat fly height profile, the ability to reduce fly heights to increase storage capacity is severely limited by the texture on the disk due to interactions of the head with the disk texture.
For files that utilize zone texturing on the disk surface to improve stiction in the start-stop, the ID flying height has been dictated by the stiction performance in the textured zone. The slider must achieve lift quickly and obtain a fly height that is higher than is necessary over the smooth data zones. However, current air bearing designs to achieve a constant fly height profiles result in the air bearing sliders flying as high in the smooth data zone as they do in the roughened textured zone. A fly height with this characteristic degrades areal density and file capacity compared to what could be accomplished if the fly height over the textured zone did not have to be considered in the air bearing design.
Improvements in the capacity and areal density of files using zone textured disks may be realized by flying high in the textured zone to maintain adequate start/stop life and stiction performance, and then flying lower in the data zones where the disk is smoother and there is no mechanical need to fly as high as in the textured zone.
It can be seen then that there is a need for an air bearing slider that can fly high in textured zones and fly lower in the data zones.
It can also be seen that there is a need for a disk drive having a disk with texture zone that require high fly heights and untextured or non-textured zones that allow low fly heights to obtain design benefits.
It can also be seen that there is a need for a disk drive which results in considerable increase in file capacity without any undue increase in file stiction.